Switching to VoIP

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Chapter 12: PSTN Trunks

How Many Dial-Tone Trunks Are Needed?

Whether you use POTS or your dial-tone is brought to you by way of SIP, you’ve got

to make sure you’ve got enough trunks for your telephony application. If you’re

building a large hosted telephony application, like a call center, you’ll probably need

loads of them. If you’re building a simple PBX in your home, you may require only

one or two. In a medium-sized office, you might need a few dozen.

The place where your PSTN interfacing occurs is your PSTN connect point. Recall

that, through VoIP, you can have voice conversations over your IP network, which

may be a WAN that spans many, many miles. This will no doubt affect the location

of your PSTN connect point, as well as the number of trunks required at that point.

In Figure 12-1, you can see how a traditional wide area voice network might look. Its

connect points are at every location where there’s a PBX.

The case for fewer trunks

You’ll use fewer PSTN trunks if you leverage your IP network. Say you’ve got three

offices—one in New York, one in Detroit, and one in Kansas City. The one in

Who provides

connectivity

ILECs, CLECs ILECs, CLECs ILECs, CLECs ILECs,

CLECs,

Internet

ILECs, CLECs Cable

company

Cost per line Most Most Moderate Low Moderate Low

Calling features Usuallycost ...